1. Technical Field
The present invention relates to driving circuit and driving method of an electro-optical device, such as a liquid crystal device, to an electro-optical device having the driving circuit, and to an electronic apparatus having the electro-optical device, such as a liquid crystal projector.
2. Related Art
As an example of an electro-optical device that is driven by this type of driving circuit, a liquid crystal device that has data lines and scanning lines wired vertically and horizontally in an image display region on a substrate and pixel units formed to correspond to intersections of the data lines and the scanning lines is exemplified.
In such a liquid crystal device, for example, a display data generating circuit generates horizontal synchronizing signals, vertical synchronizing signals, and display data based on a source signal, which is supplied from a personal computer, a video cassette recorder, or the like. Then, the driving circuit drives the respective pixel units based on the horizontal synchronizing signals, the vertical synchronizing signals, and display data. Moreover, in general, the horizontal synchronizing signals are generated such that an interval between output timings of two continuous horizontal synchronizing signals, that is, one horizontal scanning period, is basically made constant on the time axis.
The present inventors have already suggested a driving method in which the image display region is divided into a plurality of partial regions by division lines according to the scanning lines and image display is performed by region scanning. That is, according to this driving method, a driving circuit generates scanning signals based on the horizontal synchronizing signals and the vertical synchronizing signals and supplies the scanning signals to the respective partial regions alternately and to the respective scanning lines sequentially. Further, image signals, which are generated by the driving circuit based on display data are supplied to the respective data lines such that, as for two partial regions in a pair among the plurality of partial regions, the pixel units of one of the two partial regions and the pixel units of the other partial region are driven based on image signals having different polarities with respect to a reference potential at the cycle at which the scanning lines are selected. According to such a driving method, when the number of partial regions is two, in one field period, which is defined by an interval between output timings of two vertical synchronizing signals, the image signals for displaying one screen are written into the respective pixel units two times, while their polarities are changed.
Japanese Unexamined Patent Application Publication No. 2004-177930 is an example of the related art.
For example, when the video standard of a display device of the personal computer is SVGA (Super VGA (Video Graphic Adapter)) and the video standard of the liquid crystal device is XGA (Extended Graphic Array), the display device and the liquid crystal device are different in the total number of pixels or the driving frequency for image display. For this reason, down-conversion or up-conversion may be performed; in this conversion, a source signal or source data having a different total number of pixels or driving frequency is converted so as to match the liquid crystal device. During the conversion, the total number of horizontal synchronizing signals may not be an integer multiple of the total number of vertical synchronizing signals. As a result, in one field period, almost all the horizontal scanning periods can be made constant, but the last horizontal scanning period may not be made constant. Specifically, in the respective field periods, the last horizontal synchronizing pulse may not have the constant interval.
The source signal, which is generated when a video tape is played on the video cassette recorder, is influenced by damage to the video tape, for example, stretching and shrinkage. For this reason, signal processing may be performed so as to make the horizontal scanning period constant. With the signal processing, almost all the horizontal scanning periods in one field period can be made constant, but the last horizontal scanning period may not have the constant interval.
As such, when the last horizontal scanning period does not have the constant interval, in the above-described region scanning method, the image signals may not be normally written into the pixel units corresponding to the scanning line, to which the last scanning signal of one field period is supplied, in the respective partial regions. This is because there exists an inconsistency because the image signals to be written into the pixel units corresponding to the scanning line, to which the last scanning signal is supplied, are written into only some of the pixel units or sufficient write time for the image signals is not secured. In particular, when an edge of one partial region, which is subjected to region scanning, is positioned at the center of the image display region or in the periphery thereof, the abnormal writing operation of the image signals described above may cause noticeable display defects.